The metal is cooking now. It's all thin sections so this will go quick. Since there's a mix of 1045 and 4140, tempering temps are slightly different. I'm shooting for RC 35. According to the books tempering temperatures for 4140 is about 200F cooler than 1045. I'm going to split the difference and go with an oven temperature of 950. I want the metal to have a durable finish but still be workable. I think we'll be ok...
Good news and bad news. Bad news first. The shaft warped very badly just past one of the donuts. I might try to salvage it by chopping 5" off the end and weld a new piece on. If I go this route it will only be for a learning experience to see if I can pull it off. I've got a bunch of that bar stock around so, a complete re-make is not a problem. If I re-make it, I will bring it and the donuts up to 500F before welding. Also, I'll drill a hole thru the end and pre-string a piece of safety wire thru it. I normally do this so it can be dunked straight in the bath but completely forgot this time around. When it was dunked, it did not go straight into the quench and that probably sealed it's doom.
The good news: All the bearing housings survived the heat treating and as you can see, the impact dent was a good size and even left a crater rim. The 1045 parts came out at RC 33. I took a 5 thou lathe pass over this one before testing it; just enough to skim the scale off. The file grabs it nicely. FWIW, the shaft (made of 4140) tested at 36.
I looked at that bent shaft for 5 minutes and said heck no... It's beyond hope. Just for grins, I tossed it in the lathe and took a skim pass. I was just planning to get a feel for how it cut and see if it produced a nice finish. Look what showed-up... Check-out the hairline crack inside the box.
Aside from that little problem, the finish is smooth as silk.
This week beat the daylights out of me but the desire to work on this dragged me out of bed at 4:45 AM to have coffee and get going on it. Several hours later, I actually made it out to the shop ...
Well, this one did not warp as much. I did something called a Marquench (kinda). After pulling from the oven at 1525F, I let it dangle and cool off until the bright red went away then, it was dunked in a brine bath with water that was pretty close to boiling temperature. After that, it was tempered and I settled on 1000F for 1 hour with a natural cool-down. Rockwell came out to 27 and no cracks and very little warpage. In a proper "marquench" the hot part would be dunked in very hot oil for a while then, transferred to a normal quench bath. The concept is to reduce temperature shock.
Turning A Long Shaft:
There is at least a whole book worth of info to be written about turning a long shaft like this. Seems like it should be easy -but many things can go wrong. Often times, a long shaft like this will start to bow as you take cuts. That's a nasty situation and all you can do (that I know of) is use a cathead or, bend the shaft straight. A center rest or follower will do you no good -matter of fact, it will make it worse and probably ruin the piece.
I'm not spinning between centers because I'm using the same trick I showed in another project which is to just grip the end with a couple teeth of the chuck jaws (oh, and how about that sexy look'n 6-jaw chuck?). I put a light shoulder on the end of the shaft so it won't push into the jaws.
The starting point was to carefully make a clean spot in the middle of the shaft for the center rest. Once that was done, the center rest was put into position then, the donuts on either side of center were cleaned-up. Once they were cleaned-up I've been using the donuts to position the center rest when working on the ends of the shaft.
Right now, the shaft is cleaned-up. For a while, I suspected the shaft was developing a bow. I backed-off on the center rest legs and used a marker to make sure it printed a circle. There was a very slight bow so, I stopped, had a coffee break then, reseated the shaft in the chuck and tailstock -and for some reason, it went away. -Thank heavens for small favors. I'm pretty sure it was the coffee that did the trick.
Here's some close-ups... Everything is about 2-4 passes away from final size and I'll catch that after sunset. It's a beautiful day outside and the dogs want to take me on my 3rd walk of the day.
So far so good. It's coming out very straight. I'm working right to left and the shaft will remain in the chuck until it's all done.
Here's an in-situ test fit showing the drive side. On the left is the thrust bearing, followed by the spring. The collar that keeps the spring in position is not made yet. There are 2 open bearings (ceramic) because I could not find a longer ABEC 5 (or equivalent) roller bearing at an affordable price. As I recall, these were about $20 each. The shaft gives the two bearings 0.0005" clearance and they glide right on. They can't be an interference fit; if they were, there's no way the spring could exert force to cause the shaft to pre-load the front taper bearing.
When making the final pass, I grew chicken feathers and the final dia came out 0.0013 larger than I called out for. It took about 10 minutes with a wide flat file and some emery cloth to get the bearings to glide on. It still came out like a mirror.
The next thing is to make sure the outside distance between the donuts is exactly 7" as per plan. That's easy. After that comes another critical diameter for the front taper bearing, followed by the taper for grinder hub then, a left hand thread at the tip.
Finally got to spend some time on this today. Here's the piece that holds the spring. It has two purposes really; one is to support the length of the spring and the other, is to serve as a spacer to enable the spring to exert force on the shaft. The spring constant was provided with the spring and the thickness of that base was designed to put 25lbs force against the shaft (and ultimately against the taper bearing). The base on this "spring sleeve" was made about twice as thick as my calculations called for. I also made the sleeve part a little longer than originally designed. Extra material is OK in this case. It can be fine-tuned when the assembly and testing begins.
Here's some action shots:
I'm really starting to like the new chuck. It's proving to be very repeatable -to the point of initial disbelief when something is first chucked-up. Also, the reason I decided to get it was to put an end to damaging the finish on parts. So far so good.
Since this piece does not need strength, it's made of 1018. As you can see, it basically cuts like warm bubble gum. You can pretty-much spin the daylights out of 1018 and it won't produce a shiny finish.
Once again, when it came time to flip the part, the chuck was holding it darn near dead on. No marks or marring of the piece at all. How nice!
So, tomorrow, I might work on some of the other smaller pieces -possibly the hub -or maybe cut the taper on the shaft. The end caps that house the bearings are too big for a 6" chuck. I have not had time this week to clean up and mount the 8", 6 jaw chuck. I want to use that to make the bearing housings. Sometime soon, I'll switch over to that and will continue my other thread about 6 jaw chucks.
So... sorry about the delays in posting but, it's been one of those knock-down, drag-out weeks.
Coming right along. The drive side shaft and components are done (except for the bearing housing). After a little checking/indicating, the shaft is nice and straight. The testing was not thorough but, at first glance, everything is well within 1/2 thou.
Yeah, yeah, I know... You're probably thinking, "hey, what's that part between the spring and thrust bearing?". Well, I went back to CAD and decided to make a change. The small spacer has a little collar that fits in the ID of the spring to keep the spring aligned. Honestly, with tension on it, I don't think it would drift out of position but, now for sure it won't. I bored the outer spring sleeve a little deeper so there is a zero-net-change in the overall dimensions. Now, when the spring tension needs to be adjusted (downward), we can shave the back of the sleeve or the back of the collar. Right now, the design started with high spring tension and it will be adjusted as needed (by shaving or shimming).
OK, time for breakfast and walk the dogs. -And a cup of coffee (that's been known to cause cancer in California).
Breakfast (and my cancerous California coffee) was good. The dogs had me out there for a long time -making sure I get my exercise.
Coming right along... The 3 degree taper was setup using the shortcut technique described in an earlier project. This does not happen often but, the initial angle was eye-balled into place and when I checked with the indicators, it was so close to dead-on, I was tempted to leave it as-is. Better judgement took over and I bumped it one more time, checked it three times and got the same reading... -Done! No kidding, I've had days were it took almost an hour to get an angle set just right.
The taper came out nicely. If you look closely, I gave myself 1/4" of extra shaft space in case the taper ever gets damaged and needs to get cut back. The boundaries were marked with a shallow groove.
The initial scrape test showed a little low spot.
With a very smooth flat file, the high areas were lightly touched and I'm calling this good.
The fit to the bearing is satisfying... It glides on perfectly up to that point then stops because it's a 0.0003" interference fit.
We'll be done here very soon. Just need to put a left-hand thread on the end then trim the excess.
Because I have not worked on the new chuck, as soon as the shaft is done, I'll start making the wheel hub to fit this odd-ball 3 degree taper.
... Don't be afraid to comment, ask questions or give constructive criticism. This website is all about sharing info and keeping the machining trade alive.
I wanted to be further along by now but, #3 son called, stranded in a local parking lot with a dead battery. We took care of that without issues.
So, it has a left handed tread now and the nut fits just fine.
Threading Quick Tip: If the chuck and leadscrew are rotating in the same direction, you will cut a right hand thread. If the leadscrew and chuck are spinning in opposite directions, it will cut a left hand thread. It makes no difference what directions they are actually spinning, it only matters which direction relative to each-other.
LOL: When I went to cut these threads, I almost made them RH because... well because I just forgot they needed to be LH. Fortunately, I only got as far an initial scratch to see if the pitch was correct. No harm done. Man, I would have been ticked...